Butadiene-propylene copolymer weight

The molecular weight of copolymers is controlled by means of the polymerization temperature. As Table VIII shows, butadiene-propylene copolymers with low Mooney viscosity are obtained at temperatures above -40 °C. A decrease of the reaction temperature increases the molecular weight. 

There are many well-known examples of industrial problems that arise in ternary systems of two polymers and a low molecular weight compound. Consider a blend of a polar elastomer (e.g., butadiene acrylonitrile copolymer, NBR) and a hydrocarbon elastomer (e.g., ethylene propylene terpolymer, EPDM (Section 1.3.2))... 

The first free radical initiated copolymerization was described by Brubakerl) in a patent. A variety of peroxides and hydroperoxides, as well as, 02, were used as initiators. Olefins that were copolymerized with CO included ethylene, propylene, butadiene, CH2=CHX (X—Cl, OAc, CN) and tetrafluoroethylene. A similar procedure was also used to form terpolymers which incorporated CO, C2H4 and a second olefin such as propylene, isobutylene, butadiene, vinyl acetate, tetrafluoroethylene and diethyl maleate. In a subsequent paper, Brubaker 2), Coffman and Hoehn described in detail their procedure for the free radical initiated copolymerization of CO and C2H4. Di(tert-butyl)peroxide was the typical initiator. Combined gas pressures of up to 103 MPa (= 15,000 psi) and reaction temperatures of 120—165 °C were employed. Copolymers of molecular weight up to 8000 were obtained. The percentage of CO present in the C2H4—CO copolymer was dependent on several factors which included reaction temperature, pressure and composition of reaction mixture. Close to 50 mol % incorporation of CO in the copolymer may be achieved by using a monomer mixture that is >70 mol% CO. Other related procedures for the free radical... 

Miscible blends are most commonly formed from elastomers with similar three-dimensional (Hansen, 1967a,b Hansen and Beerbower, 1971) solubility parameters. An example of this is blends from copolymer elastomers (e.g., ethylene-propylene or styrene-butadiene copolymers) of slightly different composition, or microstructure. When the forces between the components of the polymer blend are mostly dispersive, miscibility is only achieved in neat polymers with a very close match in Hansen s three-dimensional solubility parameter (Hansen, 1967a,b Hansen and Beerbower, 1971), such that small combinatorial entropy for high molecular weight elastomers can drive miscibility. 

Polypropylene (PP) and polystyrene (PS) are important commodity polymers however, blertds of PP and PS are immiscible and several reports describe the use of commercial block copolymers such as styrene—butadiene—styrene (SBS), styrene-ethylene—butadiene—styrene (SEBS), styrene-ethylene—propylene (SEP), and styrene—isoprene—styrene (SIS) as nonreactive compatibilizers to achieve a finer morphology and improved performance in their blends (Bartlett et al. 1981 Radonjic et al. 1998 Hlavata et al. 1999 Raghu et al. 2003). However, the block copolymers may tend to form micelles due to their high molecular weight... 

Block copolymers with incompatible blocks which are able to microphase separate are good candidates for PSA properties. Indeed, blends of ABA triblocks and AB diblocks, where the rubbery midblock of the ABA is the majority phase and the glassy endblocks self organize in hard spherical domains and form physical crosslinks, are widely used as base polymers for PSA. The actual adhesives are always compounded with a low molecular weight tackifier resin able to swell the rubbery phase and dilute the entanglement network. Linear styrene-rubber-styrene copolymers, with rubber being isoprene, butadiene, ethylene/propylene or ethylene/butylene, are the most widely used block copolymers in this category. 

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